Effect of titanium on the microstructure and hardness uniformity of non-quenched and tempered prehardened steel for large-section plastic mould

Abstract

Two non-quenched and tempered (NQT) prehardened plastic mould steels, differing by titanium content, were produced to have good hardness uniformity in large sections (485 × 970 and 465 × 1325 mm 2 ). The effect of titanium on continuous cooling transformation curves, hardness uniformity and microstructure (grain size, phase constituents) were studied. It was found titanium had refined the grain size of NQT steel by the pinning effect of Ti (C, N) at grain boundaries, and titanium also effectively postponed the nucleation of proeutectoid ferrite in intercritical region. Using finite element method, the cooling rate from core to surface along longitude direction of the steels was predicted. The results indicated that the NQT steel with titanium had better process adaptability than that of NQT steel without titanium. Compared with production of NQT steel without titanium, production for NQT steel with titanium can largely save the production cost by shortening the production cycle and reducing the resources.

Microstructure of Ultrafine Acicular Bainite and Mechanical Properties of 3Cr2MnNiMo Mold Steel during Austempering

“…[ 2,3 ] Typically, it is provided after quenching and tempering (QT) treatment and no additional heat treatment is required after machining. [ 4 ] During the service stage, owing to the repeated opening and closing of the mold and the high‐pressure flow of the plastic liquid, plastic mold steel is subjected to large external mechanical stress. To satisfy complex working conditions, 3Cr2MnNiMo steel should have sufficient strength, toughness, and ductility, which are closely related to the corresponding microstructure.…”

“…It is known that QT treatment consumes much energy and resources in steel factories. [ 4 ] Liu [ 7 ] reported that as the tempering temperature increased from 500 to 650 °C, the strength of 718H mold steel decreased, but the impact energy and elongation increased. The effect of tempering temperature on strength and toughness was contrary.…”

Microstructural Evolution in Large-Section Plastic Mould Steel during Multi-Directional Forging

“…During the fabrication of large plastic mould steel blooms, the low impact toughness of the product is a major quality issue. Through microstructural analysis, this phenomenon is attributed to the coarse grain and nonuniform grain size [1][2][3]. As the most important manufacturing process for plastic mould steel, microstructural control in free forging processes determines product quality.…”

Improvement of Strength-Toughness-Hardness Balance in Large Cross-Section 718H Pre-Hardened Mold Steel

“…Pre-hardened mold steel, such as the medium-carbon low-alloyed steel family AISI P20 and its derived varieties DIN 1.2738 (German grade) and 718 (Swedish grade), has been widely used in industry. Usually, the AISI P20 family is known as quenching and tempering (QT) pre-hardened steel for plastic mold, because it is delivered as a QT condition from the steelworks to the mold producers and needs no further heat treatment after a mold has been machined [ 3 ]. Manufacturers only need to rough and finish it by a milling and grinding processes.…”