David Porter

• Professor
• Retired at University of Oulu

A novel method is developed to estimate the r-values or plastic strain ratios of ferritic and austenitic stainless steel. The r-values are calculated based on SEM-EBSD measurements conducted on different planes over the entire thickness of the material and for a substantial width. The mean grain orientations of the grains are used in the computatio...

Ferritic-austenitic duplex stainless steels are known to offer favorable combinations of good mechanical properties and corrosion resistance to be used for structural purposes. Lean duplex grades have already been introduced for consideration to replace standard 18−8 austenitic stainless steels in various industrial applications. Ferrite and austen...

A novel processing route comprising thermomechanical rolling followed by direct quenching and partitioning (DQ&P) was designed for developing tough, ductile, ultrahigh strength steels using 0.4 wt% carbon steels. A preliminary characterization of a laboratory-rolled, high-silicon DQ&P steel revealed an excellent combination of mechanical properties...

Bendability is an important property of ultrahigh-strength steels since the typical applications of such materials include structures manufactured by air-bending. Conventional methods to evaluate bendability, such as the bending test according to the standard VDA-238 or the conventional tensile test do not provide sufficient information to evaluate...

A systematic study has been conducted on a 17% Cr dual stabilized ferritic stainless steel (FSS) to study the evolution of texture during hot‐rolling and its effect on ridging resistance after cold‐rolling and annealing. Hot rolling was carried out on a 4‐high laboratory rolling mill with finishing temperatures in the range 1000 °C to 810 °C to cov...

The coverpage illustrates the effect of casting structure on the micro-texture and severity of ridging in stabilized ferritic stainless steels (FSS). Equiaxed grain ratio in the casting structure enhances the resistance to ridging in FSS. In this study by Suresh Kodukula and co-workers, calcium treatment and EMS effect on casting structure and FSS...

The cover image illustrates the effect of casting structure on the micro‐texture and severity of ridging in stabilized ferritic stainless steels (FSS). Equiaxed grain ratio in the casting structure enhances the resistance to ridging in FSS. In this study by Suresh Kodukula and co‐workers, article number 2000445, calcium treatment and EMS effect on...

Grain refinement has been widely used to enhance the hardness and toughness properties of metallic materials. However, the effect of prior austenite grain refinement on the final martensitic microstructure and wear performance of steels is not yet fully understood. In this study, induction hardening treatment with heating rates in the range 50 - 50...

The underlying mechanism of dislocation substructure formation in a tensile deformed fine-grained high-Mn steel is reported using transmission electron microscopy. A cross-slip assisted dislocation truncation mechanism was revealed that formed strings of dislocation loops at early strain, which were also retained at fracture strain. Planar glide pr...

Ridging means the appearance of surface profile undulations, i.e. peaks and valleys, as a result of plastic strain. The reasons for the different ridging behaviour of industrially produced, stabilized ferritic stainless steel sheets (EN 1.4509) have been investigated after straining in the rolling and transverse directions with low and high resista...

Bending behavior of a new thermomechanically processed low-alloy steel containing 0.40 wt.% carbon has been investigated. The processing included laboratory hot rolling to 10 mm thick strips followed by direct quenching to different quench-stop temperatures followed by slow furnace cooling to room temperature stimulating hot strip mill processing....

Although quenched and partitioned (Q&P) steels are traditionally alloyed with Si, its precise role on microstructural mechanisms occurring during the partitioning process is not thoroughly investigated. In this study, a systematic investigation has been carried out to reveal the influence of Si on austenite decomposition, phase transformation and c...

The effect of austenite deformation on carbon partitioning and transformation to athermal and isothermal martensite, and bainite during quenching and partitioning (QP) is described for three steel compositions: Fe-0.3C-0.6Si-1.1Al, Fe-0.3C-1.0Si and Fe-0.3C-0.5Si-0.5Al. Microstructures were characterized using SEM-EBSD, TEM and XRD. Austenite decom...

surface profile measured with 3D optical profilometer (raw data). This file could be used to calcualte the ridging index with the attached script file.

Measurement file of raw surface profile (80mm) length using 2D Surfcom SD-2000. Input file to calculate the ridging index

Source code/script file in Scilab. Copy paste the script and save it as *.sce files. Use either example 2D measurement or 3D measurement file to calcualte the ridging index.

A new method to calculate the plastic anisotropy r-values of austenitic and ferritic stainless steels has been developed. The mean orientation of individual grains is obtained from SEM-EBSD data and r-values for individual grains are calculated by weighting all slip systems according to their Schmid factors. Calculated and measured r-values are in...

Titanium and niobium are added to ferritic stainless steels (FSS) to enhance their surface and mechanical properties. The use of titanium to obtain FSS sheets that are resistant to ridging due to the formation of equiaxed rather than columnar grains during solidification is well established. However, the use of titanium results in clogging the subm...

Herein the effects of molybdenum and niobium on the microstructures and mechanical properties of laboratory‐rolled and direct‐quenched and direct‐quenched and tempered steels are revealed. The microstructures are martensitic with yield strength of 766–1119 MPa in direct‐quenched condition and 632–1011 MPa in direct‐quenched and tempered condition....

Cyclic behavior of a high-Mn austenitic steel with fine (~2 µm) and larger (~5 µm) grains was investigated under high-cycle bending fatigue at room temperature. Microhardness initially increased as a sign of cyclic hardening until 20,000 cycles and saturated thereafter. Deformation mechanisms varied widely in grains, depending on their sizes. Stack...

The effect of as-cast structure and macrosegregation on the mechanical properties of a direct-quenched low-alloy martensitic ultrahigh-strength aluminum killed and calcium treated steel cast at different superheats was studied. Samples from the castings were laboratory hot rolled with two different finishing rolling temperatures to distinguish the...

A new method to quantify the ridging phenomenon in ferritic stainless steels has been developed based on the evaluation of surface profiles after the tensile elongation of 100 mm wide sheet specimens. The ridging components of the surface profiles are extracted by a tailored spline filtering procedure. A ridging index is proposed to quantify the se...

The bending properties of a new thermomechanically processed medium-carbon (0.40 wt% C) low-alloy steel, intended for the slurry transportation pipeline application, have been investigated. The studied material was hot-rolled to 10 mm thick strips followed by direct quenching to two different quench-stop temperatures (QST) of 560 °C and 420 °C. The...

Low-carbon, low-alloy steels undergo auto-tempering and carbon partitioning to austenite during quenching to martensite. The microstructures of two such steels quenched at two cooling rates have been evaluated using electron microscopy to characterise lath and carbide precipitate morphologies, and the results have been compared with theoretical pre...

This paper focuses on understanding the effect of niobium content on the phase transformation behavior and resultant mechanical properties of thermomechanically rolled and direct-quenched low carbon steels containing 0.08 wt.% carbon. Investigated steels contained three different levels of niobium: 0, 0.02 and 0.05 wt.%. The continuous cooling tran...

The sensitization of austenitic stainless steels is dependent on various factors such as chemical composition, heat treatment temperature and time. To study these effects, the degree of sensitization in five austenitic stainless steel compositions that were subjected to isothermal heat treatments in the temperature range 550 - 820 °C has been deter...

The effect of chromium content and prior hot deformation of the austenite on the continuous cooling transformation (CCT) diagram of a newly developed low-carbon bainitic steel has been studied using dilatometer measurements conducted on a Gleeble 3800 simulator with cooling rates ranging from 2-80 °C/s. After austenitization at 1100 °C, specimens w...

In order to impart superior mechanical properties to medium carbon carbide-free bainitic steels, an innovative approach has been adopted to extensively refine the bainitic ferrite plate thickness. Unlike controlled deformation in the no-recrystallization regime above the Ar3 temperature, an attempt has been made in this study to carry out low tempe...

The effect of electroslag remelting (ESR) with CaF2-based synthetic slag on the microstructure and mechanical properties of three as-quenched martensitic/martensitic-bainitic ultrahigh-strength steels with tensile strengths in the range of 1250-2000 MPa was investigated. Ingots were produced both without ESR, using induction furnace melting and cas...

The microstructural mechanisms operating during the decomposition of austenite in a high-Si, medium‑carbon steel (Fe-0.53C-1.67Si-0.72Mn-0.12Cr) subjected to quenching and isothermal holding at temperatures above and below the martensite start (Ms) temperature for times up to 1 h have been investigated using a Gleeble 3800 thermomechanical simulato...

Offshore steels for cold climate conditions require not only relatively high strength to improve the cost-efficiency of the structures, but also excellent toughness at low temperatures to guarantee the safety of the structures in harsh environments. The most challenging locations to fulfil both requirements are in the welded joints of these steels...

As-quenched low-carbon martensitic steels (<0.2 wt.% C) contain auto-tempered carbides. Auto-tempering improves the work hardening and upper-shelf impact energy; however, an efficient characterization method to determine the degree of auto-tempering has not been available. This paper demonstrates an efficient image processing tool that calculates t...

Abstract Purpose: The purpose of this work is to determine the induction hardening behavior of a new steel composition. For this purpose, Flux2D commercial software together with a Gleeble thermomechanical simulator has been used to numerically and physically simulate the material properties profile of an induction hardened slurry transportation...

The effect of total applied strain (TAS) and finish forging temperature (FFT) on the microstructure and precipitation kinetics of a newly developed low‐cost, low‐alloy CrNiMoWMnV ultrahigh‐strength steel has been investigated. A Gleeble 3800 thermomechanical simulator was used to simulate the hot forging process and its influence on the precipitati...

Featured Application The current results can be used as a guideline for the production of high-strength low-carbon bainitic steels with high impact toughness. Abstract The effect of chromium content in the range of 1 wt.%–4 wt.% on the microstructure and mechanical properties of controlled-rolled and direct-quenched 12 mm thick low-carbon (0.04 wt...

Hardness has been considered the main factor controlling the abrasive wear of steels. However, microstructure also affects the wear behavior. Four steels with different microstructures were produced with a Gleeble 3800 thermomechanical simulator and tested for abrasive wear behavior. Different cooling rates and heat treatments were applied to obtai...

Sheared edge ductility plays a critical role in many automotive and structural applications. The effect of microalloying elements on the microstructure, mechanical properties, sheared edge quality and hole expansion properties of six thermomechanically laboratory hot rolled and coiled, approximately 4 mm thick, precipitation hardened ferritic steel...

Auto-tempering is a feature of the technologically important as-quenched low-carbon martensitic steels. The focus of this paper is on the morphology of the martensite and the orientation of the last forming untempered regions in relation to the earlier formed auto-tempered martensite in both small and large austenite grains. A low-carbon martensiti...

The effect of grain size in the range 72 to 190 μm and carbon content in the range 0.105–0.073 wt.% on the intergranular corrosion of the austenitic stainless steel 301 has been investigated. Grain boundary chromium depletion has been studied directly using energy dispersive X-ray spectroscopy combined with scanning transmission electron microscopy...

Featured Application Potential wear-resistant steel for harsh environments in agricultural sector, i.e., chisel ploughs and disc harrows. Abstract In this paper, the effects of different tempering temperatures on a recently developed ultrahigh-strength steel with 0.4 wt.% carbon content were studied. The steel is designed to be used in press-harde...

The cleanliness of ultrahigh-strength steels (UHSSs) without and with electroslag remelting (ESR) using a slag with the composition of 70% CaF2, 15% Al2O3 and 15% CaO has been studied. Three experimental heats of UHSSs with different chemical compositions were designed, melted in an induction furnace and refined using ESR. Cast ingots were forged a...

The effect of microalloying elements on the prior austenite grain growth of slab materials during slab reheating has been investigated. The investigated materials were laboratory castings with two levels of carbon (0.05 and 0.09 wt.%) and different combinations of microalloying elements, such as V, Nb, Mo and Ti. Experimental results were compared...

A model for static recrystallization by Zurob et al. [1] has been fitted to experimental stress relaxation [2] data obtained on a low-alloyed steel using a Gleeble thermomechanical simulator. The model has been implemented as an algorithm that calculates the stress relaxation as a function of time, including physical descriptions of the recovery an...

Computer simulations of steel microstructural development provide a powerful tool, which can form the basis of mechanical property predictions. However, in order to create detailed understanding of the factors affecting the properties, the model should predict microstructural evolution during cooling. The present study compares the results of cellu...

The degree of sensitization in an austenitic stainless steel, has been measured using double loop electrochemical reactivation tests, and the measured values compared with predictions based on grain boundary chromium depletion characteristics obtained using the precipitation and diffusion modules of Thermo-Calc. In order to quantitatively predict C...

With the aim of improving the strength and impact toughness combination of two ultrahigh-strength quenched and tempered steels, the effect of high-temperature austenitization and quenching prior to conventional austenitization, quenching and tempering at 200 °C has been investigated. The CrNiMoWMnV steels concerned had carbon contents of 0.18 and 0...

Double Loop Electrochemical Potentiokinetic Reactivation testing has been employed to experimentally determine the degree of sensitization (DOS) of an austenitic stainless steel subjected to isothermal heat treatment for various times in the temperature range 700–820°C. For the different heat treatment conditions, the chromium concentration profile...

The direct quenching of low-carbon steels after thermomechanical processing on hot strip mills is able to produce both strong and tough coiled plate without the need for subsequent tempering. The process is energy and time efficient with relatively low emissions when compared to conventional reheating, quenching and tempering. For some applications...

Numerical and Gleeble experimental data are combined to predict potential microstructure and hardness profiles through the wall thickness of an induction hardened slurry transportation pipe made of a recently developed 0.4 wt% C, Nb-microalloyed steel. The calculated thermal history of various positions through the wall thickness of an industrial p...

Flux2D commercial software together with a Gleeble thermomechanical simulator has been employed to numerically and physically simulate the material properties profile of an induction hardened slurry transportation pipe made of a recently developed 0.4 wt.% C, Nb-microalloyed steel. After calculating the thermal history of a 400 mm diameter, 10 mm t...

A large number of thermodynamic simulations has been used to design a new Nb-Ti dual stabilized ferritic stainless steel with excellent creep resistance at 1050°C through an optimal volume fraction of Laves (η) phase stabilized by the alloying elements Nb, Si and Mo. By raising the dissolution temperature of the phase, which also corresponds to the...

The effects of different sample preparation techniques on a set of laboratory hot-rolled and thermally cycled ferritic-austenitic stainless steels containing 19–20 wt.% Cr have been studied. The differences in chemical composition led to different volume fractions of ferrite and austenite and austenite stabilities, which were characterized using co...

The influence of cooling rate on the microstructure and mechanical properties of two new ultrahigh-strength steels (UHSSs) with different levels of C, Cr and Ni has been evaluated for the as-cooled and untempered condition. One UHSS had higher contents of C and Cr, while the other one had a higher Ni content. On the basis of dilatation curves, micr...

The influence of cooling rate on the microstructure and mechanical properties of two new ultrahigh-strength steels (UHSSs) with different levels of C, Cr and Ni has been evaluated for the as-cooled and untempered condition. One UHSS had higher contents of C and Cr, while the other one had a higher Ni content. On the basis of dilatation curves, micr...

The effect of hot-mounting for metallographic studies of as-quenched low-carbon martensitic steels has been studied. Hot-mounting is typically carried out at 150-200 • C, i.e., a low-temperature tempering regime. Cold-and hot-mounted specimens from an as-quenched low-carbon auto-tempered steel were examined using a scanning electron microscope and...

This article studied the effect of molybdenum and niobium on the microstructures and mechanical properties of laboratory control rolled steels based on grade 22MnB5. The constructed continuous cooling transformation diagrams revealed that an addition of Mo significantly increased the hardenability. Especially in the case of austenite compressed bel...

Electrochemical impedance spectroscopy (EIS) has been used to detect sensitization in austenitic stainless steels that are heat treated in the temperature regime 600-820 °C to produce different degrees of sensitization in the material. The tests were conducted at five different DC potentials in the transpassive region. The quantitative determinatio...

The influence of chemical composition and processing parameters on the microstructure and bendability of three thermomechanically rolled and direct‐quenched wear resistant steel plates is studied. Overall, the bendability of the steels is good, but there are exceptions that are given special attention. The prior austenite condition and final micros...

The direct quenching process is an energy- and resource-efficient process for making high-strength structural steels with good toughness, weldability, and bendability. This paper presents the results of an investigation into the effect of molybdenum and niobium on the microstructures and mechanical properties of laboratory rolled and direct-quenche...

The induction hardening behavior of a new, hot-rolled 0.4 wt% carbon steel with the two different starting microstructures of upper and lower bainite has been simulated using a Gleeble 3800. The effect of heating rate in the range 1–500 °C/s on austenite grain size distribution has been rationalized. Dilatometry together with Scanning Electron Micr...

In the direct quenching and partitioning (DQ&P) process, tough ultra-high-strength steel is made by combining thermomechanical processing with quenching and partitioning to obtain martensite toughened by thin films of retained austenite. The hot rolling stage with deformation and recrystallization between the rolling passes affects the state of the...

A new experimental steel containing in weight percent 0.3C-2.0Mn-0.5Si-1.0Al-2.2Cr and 0.3C-1.9Mn-1.0Si-1.0Cr was hot rolled in a laboratory rolling mill and directly quenched within the martensite start and finish temperature range. It was then partitioned without reheating during slow furnace cooling to achieve tensile yield strengths over 1100 M...

The segregation of alloying elements that occurs during the solidification of steel leads to microscale and macroscale microstructural heterogeneity that can cause anomalous mechanical behaviour. The centreline macrosegregation of a cast and its increased inclusion content are usually considered to be particularly detrimental in the case of convent...

In high- and ultrahigh-strength steel welding, interpass cooling time is an important factor affecting productivity and welding costs. Usually, welding heat input is restricted to meet the relatively short recommended cooling times between 800 and 500 °C (t8/5), which are prescribed by the need to meet weld strength and toughness properties. This,...

Corrigendum

Recent advances show that tough as-quenched ultra-high-strength steels in fully and partially martensitic conditions demand proper control of the effective coarse grain size, which is the key microstructural parameter controlling the toughness in the ductile-brittle transition region. The most effective way to reduce this grain size and texture com...

The induction hardening behavior of a new, hot-rolled 0.4 wt.% carbon steel with the two different starting microstructures of upper and lower bainite has been simulated using a Gleeble 3800. The effect of heating rate in the range 1 - 500 {\deg}C/s on austenite grain size distribution has been rationalized. Dilatometry together with Scanning Elect...

This work explores the effect of heating rate on the prior austenite grain size and hardness of a thermomechanically processed novel niobium-microalloyed 0.40 % carbon low-alloyed steel intended for use in induction hardened slurry pipelines. The aim was to identify the heating rates that lead to the maximum hardness, for high wear resistance, and...

Using a novel TMR-DQP processing route, two ultrahigh-strength steels have been developed with yield strengths up to 1100 MPa combined with good uniform and total elongations and low-temperature impact toughness. Processing involved thermomechanically controlled rolling including significant reductions below the recrystallization stop temperature (...

The effect of shot blasting on the bendability of two tempered trial ultrahigh-strength steels has been studied by comparing the bending behaviour of otherwise identical plates with and without shot blasting. The yield strength of the studied 10 mm thick trial steel was 700 MPa and 7.5 mm trial steel 1100 MPa. The local microstructures below the di...

High strength and sufficient toughness are key requirements for modern high-performance structural steels. In an attempt to develop a suitable estimation of impact toughness transition temperatures for as-quenched steels, we investigated the determiners of low-temperature toughness with a group of thermomechanically rolled direct-quenched steels wi...

The cleanness, microstructure and mechanical properties of a newly developed CrNiMoWMnV ultrahigh-strength steel with and without electroslag refining (ESR) with 70% CaF2, 15% Al2O3 and 15% CaO have been studied. This steel was designed and melted in an air induction furnace followed by refining using ESR. Cast ingots with and without ESR were forg...

Due to the volume change accompanying the fcc to bcc or bct crystal structures in steels, it is a common practice to determine phase transformation temperatures using dilatometry. The martensite start temperature (Ms) is often of particular interest. Experimentally, it is found that the start of the martensite transformation is not indicated by a s...

This paper presents a novel TFT (tuning fork test) stress corrosion testing method, which was developed for classifying martensitic high‐strength steels. The novel method was developed by applying finite element calculations to optimize a tuning fork geometry to enable accurate stress adjustment with simple inexpensive equipment. Different steels w...

The ever-increasing demand for better steel quality necessitates the development of cleaner steels. Controlling the as-cast structure, segregation and the number, size, morphology and chemical composition of non-metallic inclusions enhances steel cleanness. This can be achieved by adjusting a wide range of operating practices throughout the steel m...

Offshore steels for cold climate conditions require not only relatively high strength to improve the cost-efficiency of the structures, but also excellent toughness at low temperatures to guarantee the safety of the structures in harsh environments. The most challenging locations to fulfil both requirements are in the welded joints of these steels...

Slurry erosion is a severe problem and a major concern for slurry handling equipment, as it leads to considerable expense caused by failures, downtime and material replacement costs. Slurry erosion is dependent on several parameters such as slurry properties, service conditions, and material properties. Hence, much high-quality research has been ai...

We present a computational method for calculating the phase transformation start for arbitrary cooling paths and for different steel compositions after thermomechanical treatments. We apply the method to quantitatively estimate how much austenite deformation and how many different alloying elements affect the transformation start at different tempe...

A computational model based on the Johnson-Mehl-Avrami-Kolmogorov equation for simulating the onset and kinetics of austenite to bainite and martensite transformation has been fitted to experimental continuous cooling data for two different steels. We investigated how deformation below recrystallization temperature affected the transformation onset...

The effects of forced cooling, meaning forced cooling rate and forced cooling finish temperature, on the tensile and impact toughness properties of simulated weld coarse-grained heat-affected zones have been studied for a commercial grade martensitic steel with a yield strength of 960 MPa. The simulations were done by using a Gleeble 3800 to give f...

The tempering of re-austenized, quenched and tempered (RAQT) martensitic steels is an extensively studied and well understood field of metallurgy. However, a similar understanding of the effect of tempering on direct-quenched (DQ) high-strength steels has been lacking. Now, for the first time, the effect of tempering in the range of 250–650 °C on t...

The effect of centerline and subsurface microstructures on the crystallographic texture of three 8 mm thick low-alloyed hot-rolled and direct-quenched ultrahigh-strength strip steels with yield strengths in the range 800 – 1100 MPa has been investigated. Detailed microstructural features were studied using LCSM, FESEM, FESEM-EBSD. In addition textu...

We present computer simulations of austenite decomposition to ferrite and bainite during cooling. The phase transformation model is based on Johnson-Mehl-Avrami-Kolmogorov type equations. The model is parameterized by numerical fitting to continuous cooling data obtained with Gleeble thermo-mechanical simulator and it can be used for calculation of...