Elucidating the Effect of Step Cooling Heat Treatment on the Properties of 2.25 Cr–1.0 Mo Steel Welded with a Combination of GMAW Techniques Incorporating Metal-Cored Wires

The prospect of using metal-cored wires instead of solid wires during gas metal arc welding (GMAW) of 2.25 Cr–1.0 Mo steels embraces several challenges. The in-service requirements for the equipment made up of these steels are stringent. The major challenge faced by the manufacturers is temper embrittlement. In the current study, the temper embrittlement susceptibility of the welded joint was ascertained by subjecting it to step cooling heat treatment. A 25 mm thick 2.25 Cr–1.0 Mo weld joint was prepared using a combination of the regulated metal deposition (RMD) and GMAW processes incorporating metal-cored wires. After welding the plates were exposed to post-weld heat treatment followed by a rigorous step cooling heat treatment prescribed by API standards. The temper embrittlement susceptibility of the weld joint was ascertained by Bruscato X-factor as well as by formulating ductile-to-brittle transition temperature (DBTT) curves by carrying out the impact toughness testing at various temperatures. Detailed microscopy and hardness studies were also carried out. It was established from the study that the X-factor value for the welded joint was 15.4. The DBTT for the weld joint was found to occur at −37 °C which was well below 10 °C. Optical microscopy and scanning electron microscopy indicated the presence of carbides and the energy dispersive X-ray spectrometry studies indicated the presence of chromium and manganese-rich carbides along with the presence of sulfur near the grain boundaries. This study establishes a base for the usage of metal-cored wires particularly in high temperature and pressure application of Cr–Mo steels.

Influence of Various Heat Treatments on Hardness and Impact Strength of Uddeholm Balder: Cr-Mo-V-Ni Novel Steel Used for Engine Construction

The construction of an engine requires optimized geometry and superb material properties in various environments. Tensile and yield strength are not the only parameters essential to consider. Hardness, impact toughness, and ductile-brittle transition temperature (DBTT) are also crucial. In this paper, Balder, Chromium-Molybdenum-Vanadium-Nickel steel with low impact toughness attested is considered. It contains both high Nickel and high Vanadium content, a rare combination among iron-based alloys. This study aims at proving that conventional heat treatment can improve its impact toughness while maintaining hardness level, exceeding its to-date performance. Steel’s exact elemental composition was checked, and material samples’ hardness and impact toughness were measured. Four heat treatments were proposed, then hardness and impact toughness were measured again. It was established that impact toughness over three times higher than marketed (57.3 J against 17 J) can be achieved with simultaneous 2 HRC points (from 46.4 HRC to 48.4 HRC) rise in hardness. Achieved parameters place examined alloy at the high-ranking position among similar steels. Occurrence of temper embrittlement was avoided. Notably, the ductile-brittle transition was not observed in any sample.

Evaluating Temper Embrittlement in HY-80 Steel Using Magnetic Barkhausen Noise and Microstructural Characterization

HY80 steel is a low-carbon steel known for embodying high strength and toughness properties. This steel is used in submarine applications. Temper embrittlement, which is the reduction of fracture toughness, occurs in steels when subject to aging and drastic temperature fluctuations. These changes occur in submarines over time while in underwater environments. During temper embrittlement, impurity atoms and carbides migrate to grain boundaries, which make the steel more susceptible to fracture. A non-destructive testing (NDT) method is desirable to assess the temper embrittlement damage in HY80. Magnetic Barkhausen Noise (MBN) is of interest as being a potential NDT method for analyzing HY80. Focusing on microstructural characterization and its effect on MBN could have implications for establishing an MBN based method to detect varied stages of temper embrittlement in HY80 steel. In this research, samples of HY80 were prepared and heat treated for 16–336 hours to mimic various degrees of temper embrittlement. Microstructural changes with heat treatment were characterized and connected to the MBN produced at each holding time. Methods consisted of performing scanning electron microscopy (SEM) and using an MBN measurement system. It was observed that as holding time increases, grain size increases and carbide density within the grains decreases. These carbides, which act as pinning sites, make it more difficult for domain walls to move, consequently affecting MBN energy.

Temper embrittlement of 9%Ni low carbon steel and nondestructive inspection by magnetic Barkhausen noise

9% Ni and low carbon steel is used in cryogenic services in oil and gas industries. The final mechanical properties are adjusted by quenching and tempering heat treatments. However, the un-correct tempering may cause temper embrittlement, with drastic decrease of toughness at cryogenic temperatures. In this study, specimens tempered at 350°C, 400°C and 450°C showed very low toughness at low temperature (-196°C) due to temper embrittlement. Specimens slowly cooled from the tempering temperature (565°C, 585°C and 605°C) also showed toughness reduction in comparison with specimens tempered at the same temperature and cooled in water. The brittle fracture was characterized by intergranular cracks and cleavage. Magnetic Barkhausen Noise (MBN) inspection was conducted to verify if this technique can be used to detect the temper embrittlement in 9Ni steels. The root mean square (RMS) of the MBN signal was higher in specimens as quenched and in specimens tempered in the temper embrittlement range (350°C-500°C) than in specimens which were correctly tempered (565°C-605°C and water cooled). Comparing specimens tempered at 565 and 585°C range and slowly cooled with those which were water cooled, the RMS(MBN) was higher in the former group, which presented the lower toughness. However, the MBN inspection could not separate specimens tempered at 605°C slowly and rapidly, which can be related to the higher austenite volume fraction measured in the specimen slowly cooled.

Effect of Charpy Impact Test on Microstructure Properties of AISI4140 Steel

In this paper, the mechanical properties and microstructures of AISI4140 low alloy steel under different tempering conditions are investigated. The samples are quenched, tempered to a martensite structure and loaded to fracture by means of Charpy machine according to standard test. Fractography analysis showed that the morphology fracture surface was changed by increasing tempering temperature. The variation of energy of Charpy impact fracture as a function of tempering temperature exhibits minimum values at 300 °C, which suggests the occurrence of temper embrittlement.