Microstructure and Mechanical Properties of Nb and V Microalloyed TRIP-Assisted Steels

The intercritical annealing and isothermal bainitic processing response was studied for three Nb and V microalloyed Transformation-Induced Plasticity (TRIP)-assisted 980 MPa grade steels. Their mechanical and microstructural properties were compared to industrially produced TRIP 800 steel. Depending on the isothermal holding temperature and microalloying, the experimental steels reached properties comparable to the reference steel. The retained austenite content did not show direct correlation to elongation properties. Niobium was found to be more effective microalloying element than vanadium in increasing the elongation properties, which were investigated by measuring true fracture strain from tensile test specimens.

The epidemiology of scaphoid fractures in Sweden: a nationwide registry study

The epidemiology of scaphoid fractures has been described in limited populations, and incidence reports have been inconsistent. We investigated the nationwide incidence of scaphoid fractures by evaluating data on 34,377 patients in the Swedish National Patient Register for the years 2006–2015 regarding diagnosis, age, sex and treatment. The data were validated in 300 random patients, and incidence rates were adjusted accordingly. Forty-one per cent of the initially diagnosed fractures were false positives. The adjusted true fracture incidence rate was 22 per 100,000 person-years. During the decade studied incidence rates decreased in younger men and increased in middle-aged women. The incidence of surgical treatment vs. non-operative treatment did not change over time. Men were treated surgically more often than women (6% vs. 3%) and had a greater risk for nonunion (3% vs. 1%).

Effect of Austenite Grain Size on the Mechanical Properties in Air-Cooled 0.1C-5Mn Martensitic Steel

In 0.1C-5Mn steels, 5%Mn addition increases hardening ability and makes 100% martensitic transformation even in air cooling without water quenching. Their Ms and Mf temperatures are in the range of 350-250°C, and subzero treatment is not needed. This makes it possible to measure Ms and Mf temperatures accurately by dilatometry. Utilizing a newly developed experimental technique that makes it possible to examine phase transformation behavior and conduct tensile testing with the same specimen, we examined these relationships with identical specimens and obtained the following results. Ms temperature decreases as much as 40 K with a decrease in austenite grain size from 254 to 30 m. Regarding martensite structure, the packet size and the block length decrease, while the lath width does not change, with the refinement of austenite grain size by about one tenth. True stress - true strain curves obtained up to fracture elucidates that the austenite refinement substantially improves true fracture strength and greatly increases true fracture strain of martensite, potentially invalidating the conventional concept of a trade-off balance between strength and ductility.

Influence of Molybdenum and Copper on the Corrosion Resistance of High Strength Austenitic Steels

Joint alloying of 0.85 to 1.1 mass% C + N raises the strength and cold work hardening of steels with 18 to 19 mass% Cr and Mn each and allows to produce them at atmospheric pressure. A yield strength of 600 MPa is combined with a true fracture stress of almost 2500 MPa and ≈ 70 % elongation. However, there is a risk of carbide/nitride precipitation during quenching of thicker cross sections after solution annealing. The addition of Mo and Cu affects the corrosion resistance as well as the precipitation. Submersion test and current density/potential tests in several aqueous solutions characterize the corrosion behaviour. Tests on intercrystalline corrosion are used to detect the precipitation as a function of quenching rate. It is shown that the C/N ratio is of key importance in improving the properties.

DYNAMIC TENSILE PROPERTIES OF IRON AND STEELS FOR A WIDE RANGE OF STRAIN RATES AND STRAIN

The tensile stress-strain curves of iron and a variety of steels, covering a wide range of strength level, over a wide strain rate range on the order of 10−3 ~ 103 s −1, were obtained systematically by using the Sensing Block Type High Speed Material Testing System (SBTS, Saginomiya). Through intensive analysis of these results, the strain rate sensitivity of the flow stress for the large strain region, including the viscous term at high strain rates, the true fracture strength and the true fracture strain were cleared for the material group of the ferrous metals. These systematical data may be useful to develop a practical constitutive model for computer codes, including a fracture criterion for simulations of the dynamic behavior in crash worthiness studies and of work-pieces subjected to dynamic plastic working for a wide strain rate range.

Stainless Austenitic CrMnCN Steels of Superior Strength Part I: Alloy Design and Properties

The solubility of nitrogen is high in stainless austenite of steels with 18 mass% of Cr and Mn each, but low in the melt. Carbon reveals the opposite behaviour. Instead of producing high nitrogen steels by pressure metallurgy (PHNS), about 1 mass% of C+N is dissolved in the melt at ambient pressure. The new cost-effective C+N steel reaches a yield strength of 600 MPa, a true fracture strength above 2500 MPa and an elongation above 70 %. Conduction electron spin resonance revealed a high concentration of free electrons. Thus, the ductile metallic character of the C+N steel is enhanced, explaining the high product of strength and toughness.

Further Analysis of Warm Prestressing (WPS) Effects: Role of Local Stress and Strain

Effect of WPS in ferritic alloys 15Kh2MFA (CrMoV) and 18MND5 increases with prestress level more rapidly than Chell’s model predicts; this observation had not been understood until now. In this work, experimental data are presented concerning behaviour of steels under simple Load – Unload – Cool – Fracture history. Chell’s model uses as input quantity true fracture toughness and predicts, for simple temperature and loading histories, apparent fracture toughness. A new proposed model based on local approach corrects value of true fracture toughness as an input quantity for Chell’s formulas. Idea of the true fracture toughness increase consists in deactivation of fracture initiation particles during preload. But another interpretation is also possible: Retarding influence of dislocation substructure formed during preload (phase L) on the cleavage microcrack growth at low temperature during loading to fracture (phase F) may cause similar effect. Universal behaviour found in both steels indicates that the second interpretation is more realistic one.