Impact toughness of an S700MC-type steel: Tempforming vs ausforming

Abstract

A B S T R A C TThe effect of different thermomechanical treatments, i.e., ausforming and tempforming, on the microstructure and mechanical properties including impact fracture behavior of high-strength low-carbon S700MC-type steel was investigated. The tempforming resulted in the development of ultrafine grained elongated grain microstructure with the transverse grain size of 530 nm, whereas the ausforming led to the formation of typical tempered martensite structure with a distance between high-angle boundaries of 1.5 µm. The tempered microstructures involved the formation of carbides with an average particle size about 50 nm and M(C, N)-type carbonitrides with average size of 10 nm. The tempformed steel exhibited the ultimate tensile strength of 1110 MPa and the impact toughness, KCV, above 450 J/cm 2 at a temperature of 293 K, and KCV of 109 J/cm 2 at liquid nitrogen temperature for impact direction perpendicular to rolling plane. In contrast, KCV of the ausformed steel was 180 and 10 J/cm 2 at 293 and 77 K, respectively. The enhancement of toughness was associated with delamination cracks which occurred in the ultrafine elongated grain structure with anisotropic properties.

Effect of Different Heat Exchange Zones on Microstructure and Properties of Ultra‐Heavy Steel Plate During Jet Quenching

“…On the other hand, the increase of large‐angle grain boundary ratio can refine the grain size. Therefore large‐angle grain boundaries can effectively reduce or prevent cleavage crack propagation, however small‐angle grain boundaries have no such effect …”

The Effect of Improved Cooling on the Microstructure and Mechanical Properties of Friction Stir‐Welded Advanced High‐Strength Dual‐Phase Steel

“…As shown in Figure 11 , the microstructure of this region is composed of elongated tempered martensite and ultrafine‐grained ferrite. It has been reported [ 35 ] that the warm deformation of tempered martensite develops an ultrafine‐grained microstructure that increases the strength of tempered martensite. In addition to tempered martensite, the initial ferrite is also severely deformed and refined.…”

Tempforming as an Advanced Processing Method for Carbon Steels

“…Tempforming, therefore, is the final processing stage for technology production of rolled steel semi-products. Originally proposed for caliber bar rolling [49], tempforming has been also revealed as a promising alternative for modified ausforming applied for plate rolling [50].…”

“…The enhancement of mechanical properties is closely related to the deformation microstructure evolved in tempered martensite during large strain warm rolling. The developed microstructure in steels subjected to tempforming is commonly characterized by highly elongated grains/sub-grains along the rolling direction [50] (Figure 7a). For instance, the transverse grain and sub-grain sizes in S700MC steel are about 500 nm and 100 nm, respectively, after warm rolling to ε = 1.5 at 650 • C [50].…”