Retained Austenite Phase Transformation and Mechanical Properties of Ph Stainless Steel by Subzero Treatment Coupling Different Aging Methods

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簡歷

基本資料

Project title

Code/計畫編號

MOST108-2221-E019-036

Translated Name/計畫中文名

深冷處理耦合不同時效方法對含殘留沃斯田相之析出硬化不銹鋼的相變態及機械性能探討

Project Coordinator/計畫主持人

Shing-Hoa Wang

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Mechanical and Mechatronic Engineering

Website

https://www.grb.gov.tw/search/planDetail?id=13123515

Year

2019

Start date/計畫起

01-08-2019

Expected Completion/計畫迄

31-07-2020

Bugetid/研究經費

1689千元

ResearchField/研究領域

材料科技

研究商用17-4 PH析出硬化型不銹鋼，不同時效參數的微觀組織發展及硬度分佈，因含有3-5 wt% Cu的麻田散鐵不銹鋼，預期會有含 Cu粒子析出而得到強化。置於兩相(δ+γ)固溶處理後，微觀組織主要由異形肥粒鐵(δ)及麻田散鐵(α')組成，均無顯示殘留沃斯田鐵相(γ)的存在。固溶後經三種不同液體，油淬、水淬、及液態氮淬火，因冷卻速率不同，隨著冷速增加，原沃斯田鐵晶粒尺寸 (PAGS)變小。經X-射線繞射分析，固溶處理後經不同冷卻速率下冷卻，全都僅單相bcc峰值存在，沒有fcc相峰值呈現，與金相結果一致。固溶後鋼材分別經水淬及液態氮淬火，進行480 °C、560 °C及 600 °C時效處理。XRD峰值結果顯示，隨時效溫度增加，殘留沃斯田鐵相(γ)的峰值小於1%，並隨時效時間增加呈逐漸降低；因殘留 γ相傾向熱穩定的共析分解γ → α + Fe3C，因而降低殘留γ相含量。時效處理後的最大尖峰硬度值發生於480 °C時效1小時。因Cu粒子與麻田散鐵基地整合性較強；隨時效溫度增加，Cu粒子成長為非整合性的ε-Cu存在，導致硬度降低。於600 °C時效5小時，觀察到不同峰值隆起，經鑑定為Cu的峰值。在相對較短的1小時及3小時的時效，未發現Cu的峰值存在，推測Cu原子需要時間聚集，成核成長成粒子。固溶處理及時效處理之鋼材，經EBSD分析，錯取向 (misorientation)皆多數集中於低角度<15°及高角度>50°範圍。固溶後經油淬及液態氮淬火，於麻田散鐵基地中顯示有微雙晶(microtwins)存在，且富Cu顆粒分佈於肥粒鐵基地中。然而，於480 °C及 560 °C時效，先前水淬固溶的鋼材中，沒有銅粒子於肥粒鐵相析出，且麻田散鐵相中有微雙晶及銅粒子出現。先前液態氮淬火固溶的鋼材，有銅粒子於肥粒鐵相析出，及9R-Cu於麻田散鐵相析出。然而，600 °C時效處理，觀察到麻田散鐵基地含有回逆沃斯田鐵 (reverted austenite)及奈米富Cu粒子共存；同時麻田散鐵與回逆沃斯田鐵相互之間符合K-S取向關係。相對高溫下，促進沃斯田鐵相 (γ)的穩定元素的擴散及偏析，是回逆沃斯田鐵的生成起因。 The microstructural development and aging reactions in a commercial 17-4 PH (precipitation-hardened) stainless steel were investigated. The 17-4 PH alloy, a martensitic stainless steel with 3–5 wt% Cu, was strengthened by precipitation hardening. After solution treatment, the microstructure of the steel consisted chiefly of lath martensite with micro-twins and allotriomorphic δ ferrite. The study focused on the influences of aging at 480 °C, 560 °C, and 600 °C, followed by H2O or liquid N2 quenching. XRD analysis showed that the structure consisted entirely of bcc phase with less than 1% residual fcc austenite peaks. The maximum hardness occurred after aging at 480 °C for 1 hour. In that sample, the Cu was supersaturated in the ferrite and twins existed in the martensite in the H2Oquenched alloy, and non-coherent with the matrix uniformly distribution in the liquid N2-quenched sample. However, after aging at 600 °C, it was found that reverted austenite and nano Cu-rich particles co-existed in the martensite, and no Cu precipitates existed in the δ ferrite. Segregation and the diffusion of the austenite stabilizing elements promoted the occurrence of the reverted austenite.

Keyword(s)

殘留沃斯田鐵
超冷處理
熱循環
潛變/時效
retained austenite
subzero treatment
thermal cycling
creep/aging

DSpace CRIS

Retained Austenite Phase Transformation and Mechanical Properties of Ph Stainless Steel by Subzero Treatment Coupling Different Aging Methods

基本資料

Description